Almost all air filter arrangements for internal combustion engines utilized a single stage air filter wherein dirty air enters the filter media on one side and emerges as clean air on the other side. Currently, there is interest in air intake filters which have spaced filter media wherein there is a first filter media for filtering out relatively large entrained particles and a second filter media for filtering out relatively small particles. By providing such an arrangement the capacity of filter elements is increased, the life of the filter elements is extended, the filter efficiency is increased and filter restriction is reduced.
Typically, the filters are arranged in tandem or series so that the second filter is aligned with the first filter whereby air passing through the first filter generally does not change direction to go through the second filter. Since the filters are separated there is now consideration given to just where the first and second filters should be placed in order to enhance the air cleaning process, preferably in an economical fashion.
While filtering air for internal combustion engines is one use to which multi-stage filters are put, such filters may be of use in filtering cabin air for vehicles or for filtering air or gases occurring in other situations such as enclosures in the form of rooms or buildings.